1. Field
The present invention relates to a write-once information recording medium capable of recording and reproducing information by using a short-wavelength laser beam such as a blue laser beam, and a display apparatus for playing back the medium.
2. Description of the Related Art
As is well known, the recent spread of personal computers and the like is increasing the importance of digital data storage media. For example, information recording media capable of digital recording and reproduction of long-time video information and audio information are presently widespread. Also, information recording media for digital recording and reproduction are beginning to be used in mobile apparatuses such as cell phones.
Many information recording media of this type have disk shapes because disks have a large information recording capacity and a high random accessibility which allows rapid retrieval of desired recorded information. In addition, disks can be easily stored and carried because they are compact and light in weight, and they are also inexpensive.
Presently, so-called optical disks capable of recording and reproducing information in a non-contact state by emission of a laser beam are most frequently used as disk-like information recording media. These optical disks mainly comply with the CD (Compact Disk) standards or DVD (Digital Versatile Disk) standards, and these two standards have compatibility.
The optical disks are classified into three types: read-only optical disks incapable of information recording such as a CD-DA (Digital Audio), CD-ROM (Read-Only Memory), DVD-V (Video), and DVD-ROM; write-once optical disks capable of writing information once such as a CD-R (Recordable) and DVD-R; and rewritable optical disks capable of rewriting information any number of times such as a CD-RW (ReWritable) and DVD-RW.
Of the optical disks capable of recording, the write-once optical disks using organic dyes in recording layers are most popular because the manufacturing cost is low. This is so because users rarely rewrite recorded information with new information when an information recording volume exceeds 700 MB (Mega Bytes), so it is practically only necessary to record information just once.
As the volume of information increases, demands have arisen for increasing the capacity and transfer rate of optical disks. The presently commercially available optical disks are CDs, DVDs, and the like. To meet the market demand for shortening the recording time of a recordable optical disk, the transfer rate of, e.g., a CD-R has been increased to 48×, and that of, e.g., a DVD-R has been increased to 16×.
To further increase the capacity of an optical disk, an optical disk called an HD DVD has been developed. The data capacity of one side of an HD DVD-ROM or HD DVD-R is 15 GB that is three times or more the data capacity of the conventional DVD, i.e., 4.7 GB. An organic dye material is used in a recording layer of this HD DVD-R as described in, e.g., Jpn. Pat. Appln. KOKAI Publication No. 2003-308630 (e.g., patent reference 1).
Unfortunately, this HD DVD is capable of recording at only a standard velocity.
If data is recorded at a high linear velocity on the HD DVD-R disk capable of standard-velocity recording, the recording signal characteristics significantly deteriorate even at, e.g., 2×. That is, the characteristics of the present recording layers make high-linear-velocity recording difficult.